Epitaxial deposition of semiconductor films on single crystal semiconductor substrates is well known. Although a variety of techniques for forming such films is known, liquid phase techniques are most pertinent to the present invention. Common to liquid phase epitaxy techniques (LPE) is the preparation of a melt of the semiconductor material which is brought into contact with the condensing surface of the substate. It is common also to clean the condensing surface and to coat the surface with a wetting agent prior to the exposure of the surface to the melt.
When it is required to form a broad area rectifying junction between the epitaxial film and the substrate, the melt is doped with impurities of a conductivity type opposite to that of the substrate. For n-type conductivity gallium arsenide in particular, p-type conductivity films are required and these films have been difficult to form uniformly over the entire area of substrates of available size. Thus, junctions of varying depths are formed in the substrates resulting in diodes of nonuniform properties.
In one type of liquid phase epitaxy technique, a measured amount of doped solution is contained in a well which is brought into contact with the condensing surface at an elevated temperature. The junction in this case is formed at a depth determined by the original depth of the solution in the well. Unfortunately, in this technique, as well as in other LPE techniques, nonuniformities in the junction depths as well as voids are formed. The problems are particularly acute in the formation of large area P-type epitaxial films for gallium arsenide light emitting diodes where low yields and quality are the rule. To be specific, nonuniformity of junction depth and the occurrence of voids at which no junction is formed at all during epitaxial deposition of p-type films on N-type gallium arsenide occurred because of the lack of uniform wetting of the condensing surface by the solution from which the film is formed.